Stabilization of synthetic polymers



United States Patent STABILIZATIQN (3F SYNTHETIC POLYMERS Roger E. Morris, Cuyahoga Fails, Ray D. Taylor, Breeirsvilie, and Robert J. Faweett, Cuyahoga Falls, Ohio,

assignors to The 1%. F. Goodrich Company, New York,

N.Y., a corporation of NewYork NoDrawing. Filed May 3, 1962, Ser. No. 192,030

15 Claims. (Ci. 26ii29.7)

This invention relates to the stabilization of synthetic polymers with certain water insoluble complexing agents and more particularly pertains to the stabilization of clefinically unsaturated synthetic rubbery polymers with certain waterinsoluble amino acids and to the novel stabilized rubbery products themselves.

The' stabilization 'of rubber and particularly unvulcanized rubber against oxidative attack or stiffening which normally occurs upon aging by the incorporation therein ofa water soluble complexing or chelating agent and an antioxidant is known. In US. PatentNo. 2,667,522, for instance, is described and claimed such a composition. The compositions described and claimed in the aforementioned patent are used as pressure sensitive adhesives and it is desirable not to have them cure or become stifi'. This reference teaches that the water-soluble chelating agents are added to the rubber to be stabilized on the-mill.

The present invention isdistinguished from the disclosure of the aforementioned prior art patent in that we add our complexing or chelating agent to an aqueous synthetic rubber latex prior to the coagulation step and the subsequently coagulated and water washed rubber shows remarkable stability even at elevated temperatures. Ithas been found that water-soluble chelating agents such asthose taught by the prior art are ineffective in our process probably because they are leached from the coagulatedrubber during the coagulation and Washing steps. On the other hand, all water insoluble chelating agents are not operative'in our invention.

We have discovered a process for stabilizing synthetic rubbery polymers against degradation caused by oxygen and other atmospheric elements, said process comprising adding to an aqueous dispersion of a synthetic rubbery polymer a small amount of at least one compound having the structure CHzCOOH wherein R is a hydrocarbon group having from 6 to 20" carbon atoms, R is an alkylene group having from 2 to carbon atoms, x is a number of from 0 to 1, y is a number of from 1 to 2, when x is 0, y is 1 and when x is 1, y is 2.

The synthetic rubbery polymers embodied herein include all rubbery polymers of conjugated diolefins and particularly rubbery homopolymers and interpolymers of butadiene-l,3 hydrocarbons such as butadiene-l,3 itself, isoprene, piperylene, 2,3-dimethyl butadiene-1,3, Z-ethylbutadiene-l,3, hexadiene-l,3, 4-methyI-L3-pentadiene, and the like and halogenated dienes such as chloroprene, bromoprene and fiuoroprene. The preferred diolefins are butadiene-1,3, isoprene, piperylene, and 2-halogenated butadiene-l,3.

In addition to the rubbery homopolymers and copolymers of the aforementioned conjugated diolefins, the interpolymers of one or more of the conjugated diolefins and up to about 50% by weight of at least one other monomer copolymerizable therewith are included within the scope ofthepresent invention. The preferred other monomers are monovinyl monomers and these include the monovinyl aromatic monomers having from 8 to18 carbon atoms,

sisting. of hydrogen, an alkyl group h avin-gfrom 1 to 6- car-bon atoms, va halogen and a cyano group, and-;R" is a hydrocarbon group having from 1 to 12 carbon atoms. Illustrative monovinylaromatic monomersembodied in the. synthetic rubbery polymers of" thisinvention arestyrene, alpha-methyl styrene, the vinyl toluenes, the.

alpha-methyl vinyl toluenes, thevinyl xylenesand the like and others.

Illustrative vinyl cyanides useful in the present inven tion include acrylonitrile, methacrylonitrile, ethacrylonitrile, vinylidene cyanide, maleic dinitrile, and the-like.

Illustrative acrylic monomers embodied herein are; methyl acrylate, ethyl acrylate, the propyl acrylates, thebutyl acrylates, the amyl acrylates, the hexyl acrylates,

cyclohexyl acrylate, phenyl acrylate, the oct-yl'acrylatesand the dodecyl acrylates, methyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, dodecylmethacrylate, ethyl alpha-cyano acrylate, ethyl alpha-bromo- Most preferred of. the acrylic monomers are the lower acrylic and methacrylicacidacrylate, and the like.

esters having from 4 to 7 carbon atoms.

The preferred synthetic rubbery polymers for this invention are those composed of units derived from the polymerization of a mixture of (1) from about 50 to by weightof a conjugated diolefin and (2) from 0 to about 50% by weight of at least one member selected from the group consisting. of styrene, acrylonitrile and a lower acrylate ester having from 4 to 7 carbon atoms. In the above-described proportions of monomers itis to be understood that when a maximum of one monomer is employed that the relative proportions of the remaining. monomers must be adjusted so that the combined weight percentageof monomers used in any single polymer will total substantially 100%.

The complexing agents, chelating'agents, or stated differently, the compoundsfcapable of forming coordination complexes with polyvalent metals, embodied herein are all substantially insoluble in water, they are soluble in or compatible with conjugated diolefinr-ubbers and they all'conform to the structure OHzCOOH wherein R, R, x and y each has the aforementioned designation. this class are the following:

Illustrative specific compounds falling into- Although the water insoluble chelating agents of this invention are effective per se in the stabilization of the synthetic rubbery polymers embodied herein, it is often desirable to include a conventional rubber antioxidant in the rubber and such inclusion is within the scope of the present invention. Normally the aqueous latex or the dispersion of the synthetic rubbery polymer which is to be protected against atmospheric deterioration will include an antioxidant which is preferably of the aromatic phenol and hindered aromatic phenol type which are Well known in the art.

The aqueous latices and dispersions of synthetic rubbery polymer embodied herein are prepared by methods well known in the art. For instance, a rubbery copolymer of about 75% by weight of butadiene-1,3 and 25% by weight of styrene is prepared in an aqueous medium in the presence of a suitable polymerization catalyst in the range of from about 15 to 40% total solids. The aqueous medium may be emulsifier free or it may contain an emulsifier. Suitable emulsifiers include conventional alkali metal soaps, sulfates and sulfonates such as sodium lauryl sulfate, the alkali metal salts of petroleum or paraffin oils, the sodium salts of aromatic sulfonic acids such as the sodium salt of naphthalene sulfonic acid, the sodium salts of dodecane-1-sulfonic acid, octadecane-lsulfonic acid, etc., aralkyl sulfonates such as sodium isop'ropyl benzene sulfonate, sodium dodecyl benzene sulfonate and sodium. isobutyl naphthalene sulfonate; alkali the. hydrochloride of diethylaminoethyldecylamine, trimethyl cetyl ammonium bromide, dodecyl trimethyl ammonium bromide, the diethylcyclohexylamine salt of cetyl sulfuric ester, and others also may be used. Preferred, however, are the-alkali metal salts of long chain carboxylic acids and alkali metal salts of aromatic sulfonic acids and the sodium salts of aralkyl sulfonates. In addition to the above and other polar or ionic emulsifiers, still other materials which may be used, singly or in combination with one or more of the above-mentioned types of emulsifiers, include the so-called non-ionic emulsifiers such as the polyether alcohols prepared by condensing ethylene oxide with higher alcohols, the fatty alkylolamine condensates, the diglycol esters of lauric, oleic and stearic acids, and others. It is also often desirable to add post-polymerization emulsifiers to the latices for improved latex stability.

The catalyst, required for satisfactory polymerization rate, may be any of those commonly employed for the polymerization of butadiene hydrocarbons including the various peroxygen compounds such as hydrogen peroxide, benzoyl peroxide, pelargonyl peroxide,'cumene hydroperoxide, tertiary butyl hydroperoxide, l-hydroxy-cyclohexyl hydroperoxide, tertiary butyl diperphthalate, tertiary butyl perbenzoate, sodium, potassurn and ammonium per-sulfate and others. Particularly preferred are the water-soluble peroxygen compounds such as hydrogen peroxide and the sodium, potassium and ammonium persulfate, the water-soluble oxidation-reduction or redox types of catalysts, and the heavy metal activated, water-soluble peroxygen and redox catalysts. Included in the list are the water-soluble persulfates; the combination of one of the water-soluble peroxygen compounds such as potassiumpersulfate with a reducing substance such vas a polyhydroxy phenol, an oxidizable sulfm compound such as sodium bisulfite, sodium sulfite closed in the Encyclopedia of Chemical Technology by Kirk and Othmer, Interscience Encyclopedia, Inc., New York, vol. 2, pages 6975, vol. 11, pages 881-887 and in the First Supplement Volume, pages 85-88.

Rubber antioxidants, and particularly those useful in synthetic rubbers, are usually needed to prevent degradation' caused by shelf aging, oxidation aided by metal catalysts, the effects of heat and light, the effects caused 'by flexing and by exposure to the atmosphere. The chemically important rubber antioxidants fall into two main classes: amines and their derivatives and phenols and their derivatives. -The power, as antioxidants, of members of each class is approximately the same, but essential difference lie in their efiectiveness in the presence of carbon black and in the degree of staining imparted to vulcanizates on exposure to light. Antioxidants probably function in rubber much as they do in other aut-ooxidizable materials to act as chain-stoppers, transfer agents, and peroxide decomposers. Some ofthe most commonly. used antioxidants in the rubber industry are phenolics such as 2,6-di-tert-butyl-p-cresol, 2,2'-methylenebis(4-methyl-6-tert-butyl phenol), 1,5-dihydroxynaphthalene, 4,4'-thiobis(3-methyl-6-tert-butyl phenol), 4,4-dihydroxy-diphenyl, 4,4 butylidenebis(3-methyl-6-te-rt-butyl phenol); amines such as the alkylated and aralkylated diphenyl amines, phenyl-l and Z-n-aphthylamines; carbonylamine reaction products such as the reaction products of aniline and acetalde-hyde, diphenylamine and acetone, phenyl-Z-naphthylamine and acetone; and heterocyclics such as Z-mercaptobenzimidazole and 5,5-dimethylacridan. Also included herein are the new phenolic antioxidants having the structure i I R2 -Q -Q Q (3113 /x :1 wherein R represents a bulky hydrocarbon group such as t-butyl, t-amyl, t-hexyl, cyclohexyl, t-pentyl, =t-octyl, phenyl and the like; R represents hydrogen and R; R 'represents an alkyl group having from 6 to 20 carbon atoms which is preferably in the meta or para position; x represents a number'of fr-oml to 3 inclusive; y represents a number of from O to 2 inclusive and the sum of the numerical value of x+y is always exactly 3, which are disclosed and claimed inthe copending patent application of Roger E.

bilized in any of the conventional ways such as by millmixing, mixing in an internal mixer such as the Banbury,

by adding the chelating agent to the rubber latex, dispersion or cement. Most preferred in the present inven tion is to add the water-insoluble chelating agent to the rubber latex and even more preferred is to mix the water- -insoluble chel-ating agent with the antioxidant and add this mixture to the latex. It is often convenient to emuls 5 sify in water a mixture of the water-insoluble chel-ating agent and antioxidant and then to add the emulsion directly to the rubber latex. The resulting stabilized latex can then be coagulated, Washed and dried in the sta'bilized condition.

6 and dried. In a similar manner chelating agents of the formula In the practice of the present invention it is desirable Whefelll R h from 17 18 carbon atoms were to use f about 0.1 to about parts by weight per prepared starting with Duomeen S and with Duomeen T. 100 parts by weight of rubber of combined phenolic The Duomeehs are marketed y the Armour p yantioxidant-rubber soluble chelating agent and it is pre- Example I ferred to use a ratio of from 0.5 to by Weight of 10 the rubber-soluble chelating agent and from 99.5 to 90% To 2000 of a 9% total Sohds latex of butadene by wight of the phenolic antioxidant in the aforemem styrene rubber contaimng about 23.5% by weight of rubtioned combined antioxidant-chelating agent. bet 0f 2 PrePard at Q m a {mxed The present invention will be further illustrated by the fatty 95 a f d Soap recipe was added an emulsion of following examples wherein the amounts of the various 5 of f' 50 of 4 aqueous Soap (sqdmm ingredients are expressed in parts by Weight unles oth tearatei solut1on. The resulting latex was then diluted Wise indicated. with distilled water to 10% total sohds and the rubber was coagulated with salt-acid treatment. The rubber crumbs PREPARATION OF CHELATING AGENTS were washed free of salt and acid with distilled water.

Dodecyliminodiacetic acid was prepared as follows: The 4 mlhlhe Mooney of these 111131963 Wtire .Chlomcetic acid (L1 mole) in 300 1 f ethanol was then determined after various intervals of oven aging at neutralized by the addition of 125 ml. of 10 N aqueous m a clryulatmg an oven- The phenolic antisodium hydroxide. Dodecyl amine (0.5 mole) was added oxidant 111 thls example has the Structure to the mixture and the solution was heated to 80 C. CH3 and the pH was maintained at from 8 to 10 by the grad- 25 ual addition of more 10 N sodium hydroxide solution until the theoretically required amount of sodium hydrox- (CH3): CH3 (5mm); ide had been added. The reaction mix-ture was then brought to room temperature and the dodecyl-iminodiacetic acid was precipitated by bringing the pH of the mixg gg fgf ture to 2 with concentrated hydrochloric acid. The prodnot was isolated by filtration and was washed twice with Stabhm None distilled water and dried to a constant weight of 141.3 g. (origi- 1 2 4 6 (94% of theory). nal) In a similar manner octadecyliminodiacetic acid was d Phenol c ant ox dant 49 47 56 74 88 P p Phenolic antioxidant plus 3% by weight of Achelating agent having the structure CuH HwBiQOOEDi 49 50 46 52 62 Phenolic antioxldant plus 3% disahcylidene CH COOH Propylene diamine 49 52 62 73 87 RNCHICH2CE2N(CH2COOH)3 u The disalicylidene propylene diarnlne 1s a known water wherein R 1s a mix re of alkyl g p h vlng an v r ge insoluble chelating agent which obviously is inoperative of 13 carbon atoms was prepared as follows: Chloroacetic and outside the scope of this invention, The substitution acid (2.24 moles) in 490 ml. of methanol was neutralized of octadecyliminodiacetic acid for the dodecyliminodi- W 3 N SOIHHOII- een CD acetic acid above gave comparable results.

(R-NHCH CH CH NH Example II wherein R is a mixture of alkyl groups having an average The Procedure deSci-ibed in Examp 16 I was followed of 13 carbon atoms, 0.25 mole) was added, the reaction except. that the biltadlene'stiirene a was one mixture was brought to 70-73 C. and the pH of the reparfid a fatty p spap recipe at 50 The phenohc action mixture was maintained at 8-10 by the addition of ammxldant used m this example has the Structure more 31% NaOH solution until the pH became fairly con- 4 stant for a period of time. The mixture was cooled and Ho C OH the product was precipitated with hydrochloric acid (pH I I I of 2). The solid was isolated by filtration, was washed C(CHS), 3 (H0113),

4 min. MooneyViscosity days at 105 C Stabilizer None 1 2 4 6 Phenolic antioxidant- 50 46 58 72 71 Phenolic antioxidant plus 3 percent Ho-omom NCHzCHzN(CHgCOOH)2 51 46 5s 69 H OOC-CH:

Phenolic antioxidant plus 10 percent Ito-onion,

NOH2CH2N(CH2000H)I 49 44 54 65 69 HOOCCH2 Phenolic antioxidantplus3porcent C|zHi5N(CHzCO0H)2 50 46 45 41 42 Phenolic antioxidant plus 1 percent Cl2H25N(CHlCO0H)2- 51 43 39 45 5D It is apparent that water soluble chelating agents, as exemplified by are not operative and are not Within the scope of the present invention. Similarly ethylene diamine tetraacetic acid (EDTA) when combined with the phenolic antioxidant and incorporated into the rubber latex showed no improve- 10 The procedure of Example II was repeated usinga different batch of the butadiene-styrene latex. The phenolic antioxidant used in this example has'the structure 1 CH3 I 20 The substitution of a chelating agent having the structure wherein R averages from 17 to 18 carbon atoms for the chelating agent shown above gave comparable results.

We claim:

1. The rubbery composition resistant to atmospheric degradation comprising a mixture of a synthetic rubbery polymer of at least 50% by weight of a conjugated diene having fr'om4 to'6 carbon atoms and the remainder another monomer'copolymerizable with said diene and a small but effective amount sufficient to protect said rubbery polymer against degradation by oxygen of at least one compound having the structure CHaOOOH R-NT N A ornooonl C(CHa): C(CH3 3 wherein R is a hydrocarbon group having from 6 to 20 4 min. Moone Viscosity,

days at 105 0. Stabilizer None 2 4 6 Phenolic antioxidant- 49 58 71 75 Phenolic antioxidant plus 3 percent CHzC O OH 46 39 39 42 C 3H2 NCHgCHzCH2N(CHgC O OHM Example IV The procedures of the preceding examples were repeated using a butadiene-styrene rubber latex prepared at 5 C. in a fatty acid soap recipe.

carbon atoms, R is an alkylene group having'from 2 to 10 carbon atoms, x is a number of from 0 to 1, yis a number of'from 1 to 2, when'x is 0, y is 1 and when x is 1, y is 2.

Stabilizer 4 min. Mooney Viscosity, Days at 105 0.

None 12 4 6 [2,4-di(alpha-methyl benzyl)phenol] 2,4-di(a1pha-methyl benzyl) phenol plus 3 percent CH1 0 O OH s)a C M I a HO -O OP--O CnHm 2 I CH3 1 C M C (C 3):

plus 3 percent CHzG O OH C13H27N CH2CH2CHZN(CH)C O OH);

0.03 percent CHaCO OH I C1s 21NGH2 CH:CH2N( 01120 O OH) 3 (based on 100 parts of rubber) N o stabilizer 9 2. The stable composition comprising a mixture of a rubbery synthetic homopolymer of a conjugated diolefin and a small but effective amount sufiicient to protect said rubbery polymer against degradation by oxygen of at least one compound having the structure wherein R is a hydrocarbon group having from 6 to 20 carbon atoms, R is an alkylene group having from 2 to 10 carbon atoms, x is a number of from to 1, y is a number of from 1 to 2, when x is 0, y is l and when x is 1, y is 2.

3. The stable composition comprising a mixture of 100 parts by weight of a synthetic rubbery polymer composed of units derived from the polymerization of a mixture of (1) from about 50 to 100% by weight of a conjugated diolefin and (2) from 0 to about 50% by weight of at least one monomer selected from the group consisting of styrene, acrylonitrile, and a lower acrylate ester having from 4 to 7 carbon atoms and from about 0.1 to 5 parts by weight based on the rubbery polymer of (3) a phenolic antioxidant and (4) a compound having the structure CHrCOOH wherein R is a hydrocarbon group having from 6 to 20 carbon atoms, R is an alkylene group having from 2 to carbon atoms, x is a number of from 0 to 1, y is a number of from 1 to 2, when x is 0, y is 1 and when x is 1, y is 2.

4. The stable composition comprising a mixture of 100 parts by weight of a synthetic rubbery polymer composed of units derived from the polymerization of a mixture of (1) from about 50 to 100% by Weight of butadiene-1,3 and (2) from 0 to 50% by weight of at least one number selected from the group consisting of styrene, acrylonitrile, and a lower acrylate ester having from 4 to 7 carbon atoms and from about 0.1 to 5 parts by weight based on the rubbery polymer of (3) a phenolic antioxidant and (4) a compound having the structure wherein R is a hydrocarbon group having from 6 to carbon atoms, R is an alkylene group having from 2 to 10 carbon atoms, x is a number of from O to l, y is a number of from 1 to 2, when x is 0, y is 1 and when x is 1, y is 2, said (3) and (4) being present in a weight ratio of from 0052995 to 1:9 respectively.

5. The stable composition comprising a mixture of 100 parts by weight of a synthetic rubbery polymer composed of units derived from the polymerization of a mixture of (1) from about 50 to 100% by weight of butadiene-1,3 and (2) from 0 to 50% by weight based on the rubbery polymer of styrene and from 0.1 to 5 parts by weight based on said rubbery polymer of (3) a phenolic antioxidant and (4) a compound having the structure OHzCOOH 6. The stable composition comprising a mixture of parts by weight of a synthetic rubbery polymer composed of units derived from the polymerization of a mixture of (1) about 77% butadiene-1,3 and (2) about 23% styrene and from 0.1 to 5 parts by Weight based on said rubbery polymer of (3) a phenolic antioxidant and (4) a compound having the structure CHzCOOH wherein R is a hydrocarbon group having from 6 to 20 carbon atoms, R is an alkylene group having from 2 to 10 carbon atoms, x is a number of from 0 to 1, y is a number of from 1 to 2, when x is 0, y is 1 and when x is 1, y is 2, said (3) and (4) being present in a weight ratio of from 0.05 19.95 to 1:9 respectively.

7. The composition of claim 6 wherein R is an alkyl group having 12 carbon atoms, x is 0 and y is 1.

8. The composition of claim 6 wherein R is an alkyl group having an average of 13 carbon atoms, R is an alkylene group having 3 carbon atoms, x is 1 and y is 2.

9. An aqueous latex of the composition of claim 1.

10. The method for preparing a stable synthetic rubbery polymer of at least 50% by weight of a conjugated diene and the remainder a monomer copolymerizable with said diene comprising adding to an aqueous latex of a synthetic rubbery polymer a small but effective amount suflicient to protect said rubbery polymer against degradation by oxygen of a compound having the structure CHzCOOH wherein R is a hydrocarbon group having from 6 to 20 carbon atoms, R is an alkylene group having from 2 to 10 carbon atoms, x is a number of from 0 to 1, y is a number of from 1 to 2, when x is 0, y is 1 and when x is 1, y is 2 and then coagulating, washing and drying the rubbery product.

11. The method for preparing a stable synthetic rubbery polymer comprising adding to an aqueous latex containing 100 parts by weight of a synthetic rubbery polymer composed of units derived from the polymerization of a mixture of (1) from about 50 to 100% by weight of a conjugated diolefin and (2) from 0 to about 50% by weight of at least one member selected from the group consisting of styrene, acrylonitrile, and a lower acrylate ester having from 4 to 7 carbon atoms, from about 0.1 to 5 parts by weight based on said rubbery polymer of (3) a phenolic antioxidant and (4) a compound having the structure CHzCOOH wherein R is a hydrocarbon group having from 6 to 20 carbon atoms, R is an alkylene group having from 2 to 10 carbon atoms, x is a number of from 0 to 1, y is a number of from 1 to 2, when x is 0, y is 1 and when x is l, y is 2 and then coagulating, washing and drying the rubbery product.

12. The method of claim 11 wherein the conjugated diolefin is butadiene-1,3.

13. The method of claim 11 wherein the weight ratio of (3) to (4) is from. 0.05 19.95 to 1:9 respectively.

14. The method of claim 11 wherein (2) is styrene.

15. The composition of claim 6 wherein R is an alkyl group having 16-18 carbon atoms, x is 1 and y is 2.

(References on following page) References Cited by the Examiner UNITED OTHER REFERENCES Schildknecht: Polymer Process, v01. X, pp. 152-153, Interscience Publishers, Inc., NY.

STATES PATENTS Davidson 260814 V V lg/Iunz fl 5 MURRAY TILLMAN, Primary Examiner.

erswo-rt M cElrOy 260 314 WILLIAM H. SHORT, Exammer.

Lew 260-534 J. ZIEGLER, Assistant Examiner. 

1. THE RUBBERY COMPOSITION RESSISTANT TO ATMOSPHERIC DEGRADATION COMPRISING A MIXTURE OF A SYNTHETIC RUBBERY POLYMER OF AT LEAST 50% BY WEIGHT OF CONJUGATED DIENE HAVING 4 TO 6 CARBON ATOMS AND THE REMAINDER ANOTHER MONOMER COPOLYMERIZABLE WITH SAID DIENE AND A SMALL BUT EFFECTIVE AMOUNT SUFFICIENT TO PROTECT SAID RUBBERY POLYMER AGAINST DEGRADATION BY OXYGEN OF AT LEAST, ONE COMPOUND HAVING THE STRUCTURE 